Light emitting device using nitride semiconductor and fabrication method of the same

ABSTRACT

A nitride based 3-5 group compound semiconductor light emitting device comprising: a substrate; a buffer layer formed above the substrate; a first In-doped GaN layer formed above the buffer layer; an In x Ga 1 — x N/In y Ga 1−y N super lattice structure layer formed above the first In-doped GaN layer; a first electrode contact layer formed above the In x Ga 1 — x N/In y Ga 1−y N super lattice structure layer; an active layer formed above the first electrode contact layer and functioning to emit light; a second In-doped GaN layer; a GaN layer formed above the second In-doped GaN layer; and a second electrode contact layer formed above the GaN layer. The present invention can reduce crystal defects of the nitride based 3-5 group compound semiconductor light emitting device and improve the crystallinity of a GaN GaN based single crystal layer in order to improve the performance of the light emitting device and ensure the reliability thereof.

This application claims priority of Korean application no. 41409/2003,filed Jun. 25, 2003, and is the national stage application ofPCT/KR2004/001480, filed Jun. 21, 2004.

TECHNICAL FIELD

The present invention relates to a nitride based 3-5 group compoundsemiconductor. More particularly, the present invention relates to anitride based 3-5 group compound semiconductor light emitting device anda fabrication method thereof capable of reducing crystal defectsoriginated from the mismatch of thermal expansion coefficient andlattice constant between a substrate and a GaN based single crystallayer grown thereon as well as improving the crystallinity of the GaNbased single crystal layer in order to improve the performance of thelight emitting device and ensure the reliability thereof.

BACKGROUND ART

GaN-based semiconductors are generally applied to optical devices suchas a blue/green LED and high-speed switching and high-power electronicdevices such as a Metal Semiconductor Field Effect Transistor (MESFET)and a High Electron Mobility Transistor (HEMT). In particular,blue/green LEDs have been mass produced lately, and their worldwidedemand is rising sharply.

A GaN-based semiconductor light emitting device is typically grown on asubstrate of sapphire or SiC. Then, a polycrystalline layer ofAl_(y)Ga_(1−y)N is grown as a buffer layer on the sapphire or SiCsubstrate at a low growth temperature. At a higher temperature, anundoped GaN layer and a Si-doped n-type GaN layer or a mixed structurethereof are grown on the buffer layer to provide the n-type GaN layer asa first electrode contact layer. Then, a Mg-doped p-type layer is formedas a second electrode contact layer thereon to produce a nitride based3-5 group compound semiconductor light emitting device. In addition, anactive layer (of a multiple quantum well structure) is interposedbetween the n-type first electrode contact layer and the p-type secondelectrode contact layer.

In the nitride based 3-5 group compound semiconductor light emittingdevice of this structure, crystal defects found in the interface betweenthe substrate and the buffer layer have a very high value of about10⁸/cm³. As a result, this degrades electrical characteristics of thenitride based 3-5 group compound semiconductor light emitting device,and more particularly, increases leakage current under reverse biasconditions, thereby causing a fatal effect to the reliability of thelight emitting device.

In addition, the crystal defects created in the interface between thesubstrate and the buffer layer degrades the crystallinity of the activelayer, and therefore disadvantageously lowers the luminous efficiency ofthe nitride based 3-5 group compound semiconductor light emittingdevice.

In the meantime, in order to improve the performance and reliability ofthe GaN-based semiconductor light emitting device, researches have beenmade for new buffer layers and various fabrication methods of GaN-basedsemiconductors have been studied.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and it is therefore an object of the present invention toprovide a nitride based 3-5 group compound semiconductor light emittingdevice and a fabrication method thereof capable of reducing crystaldefects of a GaN based single crystal layer as well as improving itscrystallinity in order to improve the performance and reliabilitythereof.

It is another object of the present invention to provide a nitride based3-5 group compound semiconductor light emitting device and a fabricationmethod thereof capable of practically realizing high brightnessperformance from an active layer of only a single quantum wellstructure.

According to an aspect of the invention for realizing the above objects,there is provided a nitride based 3-5 group compound semiconductor Lightemitting device comprising: a substrate; a buffer layer formed above thesubstrate; a first In-doped GaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer formedabove the first In-doped GaN layer; a first electrode contact layerformed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer; an active layer formed above the first electrode contact layerand functioning to emit light; a second In-doped GaN layer; a GaN layerformed above the second In-doped GaN layer; and a second electrodecontact layer formed above the GaN layer.

According to another aspect of the invention for realizing the aboveobjects, there is provided a nitride based 3-5 group compoundsemiconductor light emitting device comprising: a substrate; a bufferlayer formed above the substrate; a first In-doped GaN layer formedabove the buffer layer; a first electrode contact layer formed above thefirst In-doped GaN layer; an active layer formed above the firstelectrode contact layer and functioning to emit light; a GaN layerformed above the active layer; and a second electrode contact layerformed above the GaN layer.

According to further an aspect of the invention for realizing the aboveobjects, there is provided a nitride based 3-5 group compoundsemiconductor light emitting device comprising: a substrate; a bufferlayer formed above the substrate; a first electrode contact layer formedabove the GaN buffer layer; an active layer formed above the firstelectrode contact layer, and including a low mole In-dopedIn_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)N well layer and anIn_(z)Ga_(1−z)N barrier layer; a GaN layer formed above the activelayer; and a second electrode contact layer formed above the GaN layer.

According to still another aspect of the invention for realizing theabove objects, there is provided a fabrication method of a nitride based3-5 group compound semiconductor light emitting device, comprising:forming a buffer layer above a substrate; forming a first In-doped GaNlayer above the buffer layer; forming a first electrode contact layerabove the first In-doped GaN layer; forming an active layer for emittinglight above the first electrode contact layer; forming a GaN layer abovethe active layer; and forming a second electrode contact layer above theGaN layer.

The advantage of the present invention is to reduce crystal defects of aGaN based single crystal layer as well as improve its crystallinity,thereby improving the performance and reliability thereof.

As another advantage, the present invention can practically realize highbrightness performance from an active layer of only a single quantumwell structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a first embodiment ofthe present invention;

FIG. 2 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a second embodiment ofthe present invention;

FIG. 3 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a third embodiment ofthe present invention; and

FIG. 4 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a fourth embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to accompanying drawings.

While preferred embodiments of the present invention will be describedin reference with the accompanying drawings, it is apparent to thoseskilled in the art that the principle of the present invention is notlimited by the disclosed embodiments thereof, but can be readilymodified into various alternatives through the addition, variation andomission of components.

First Embodiment

FIG. 1 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a first embodiment ofthe present invention.

As shown in FIG. 1, a nitride based 3-5 group compound semiconductorlight emitting device has a cross-sectional structure including a bufferlayer 104 grown on a substrate 102, a first electrode contact layer 108made of an n-type GaN layer (codoped with Si and In) and a secondelectrode contact layer 120 of an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure. Herein, the first and second electrode contact layers108 and 120 are provided with electrodes (not shown), respectively, infollowing process steps so that external voltage can be applied theretovia the electrodes.

The nitride based 3-5 group compound semiconductor light emitting deviceof the present invention also has an active layer 116 of a quantum wellstructure which is interposed between the first electrode contact layer108 and the second electrode contact layer 120 to form ahetero-structure. The active layer 116 includes a low mole In-doped GaNlayer 110, an In_(x)Ga_(1−y)N well layer 112 and an In_(x)Ga_(1−x)Nbarrier layer 114.

In addition, the nitride based 3-5 group compound semiconductor lightemitting device also has an In-doped GaN layer 106 formed between thebuffer layer 104 and the first electrode contact layer 108 and a p-typeGaN layer 118 formed between the In_(x)Ga_(1−x)N barrier layer 114 andthe second electrode contact layer 120.

A fabrication method of the nitride-based 3-5 group compoundsemiconductor light emitting device of the present invention will bedescribed as follows:

First, a GaN buffer layer 104 is formed on a sapphire substrate 102 at alow growth temperature. Then, the buffer layer 104 of the GaN-basedsemiconductor may be grown into an InGaN/GaN super lattice structure anda structure of In_(x)Ga_(1−x)N/GaN andAl_(x)In_(y)Ga_(1−x,y)N/In_(x)Ga_(1−x)N/GaN at the low growthtemperature.

The buffer layer 104 formed on the substrate 102 as above canefficiently restrain crystal defects induced from the mismatch ofthermal expansion coefficient and lattice constant between the substrate102 and a GaN-based single crystal layer grown on the substrate 102,thereby producing a high quality GaN-based semiconductor.

More particularly, in the process step of growing the GaN buffer layer104, H₂ and N₂ carrier gases, TMGa, TMIn and TMAl sources and NH₃ gasare fed at a temperature of about 500 to 700° C. to grow the GaN bufferlayer 104.

Then, an In-doped GaN layer 106 and a GaN layer 108 containing Si and Incodoped therein are grown on the buffer layer 104 at a high growthtemperature. Herein the Si/In-codoped GaN layer 108 is used as a firstelectrode contact layer.

More particularly, in the process step of growing a GaN based singlecrystal layer of the GaN-based semiconductor, the GaN based singlecrystal layer is grown by feeding TMGa, TMIn and TMAl sources at atemperature of about 900 to 1100° C. with an MOCVD apparatus, in whichSiH₄ gas may be used as a Si doping source, and TMIn may be used as anIn doping source.

The active layer 116 for emitting light in a desired wavelength rangeincludes a single quantum well. More particularly, the low mole In-dopedGaN layer 110 of the active layer 116 is grown in the range of 10 to 500Å. More preferably, the low mole In-doped GaN layer 110 is grown to athickness in the range of 50 to 300 Å. The content of the low moleIn-doped GaN layer may be expressed as In_(x)Ga_(1−x)N (0<x≦0.2). Then,a quantum well layer of an In_(y)Ga_(1−y)N well layer 112 and anIn_(z)Ga_(1−z)N barrier layer 114 of different In content is grown onthe low mole In-doped In_(x)Ga_(1−x)N layer 110 to form the activelayer.

In the process step of growing a single quantum well structure of theactive layer 116, the low mole In-doped In_(x)Ga_(1−x)N layer 110, theIn_(y)Ga_(1−y)N well layer 112 (0<y≦0.35) and the In_(z)Ga_(1−z)Nbarrier layer 114 (0<z≦0.2) are grown by flowing TMGa, TMIn and TMAlsources on N₂ or H₂+N₂ carrier gas in NH₃ atmosphere. In this case, thelow mole In-doped In_(x)Ga_(1−x)N layer 110 has a thickness of about 10to 500 Å, and its surface is uniformly grown in a spiral mode. Further,at a surface growth temperature of about 700 to 800° C., the InGaN welllayer 112 for emitting light is grown to a thickness of 5 to 30 Å andthe InGaN barrier layer 114 is grown to a thickness of 50 to 500 Å.

In addition, in order to realize high brightness light emitting deviceperformance, it is necessary to maintain the uniform spiral mode fromthe surface of the low mole In-doped In_(x)Ga_(1−x)N layer 110 to theInGaN barrier layer 114. If above growth conditions are satisfied, apractical high brightness light emitting device can be fabricatedthrough the formation of an active layer having a single quantum wellstructure as well as having a multiple quantum well structure. Ofcourse, the multiple quantum well structure can be adopted in cases thatother parts are the same.

In the meantime, the content distribution of dopant in the low moleIn-doped In_(x)Ga_(1−x)N layer 110, the In_(y)Ga_(1−y)N well layer 112and the In_(z)Ga_(1−z)N barrier layer 114 can be adjusted as follows:The In content of the low mole In-doped In_(x)Ga_(1−x)N layer 110 isadjusted to be lower than that of the In_(z)Ga_(1−z)N barrier layer 114.The doped In contents x, y and z may be expressed as 0<x<0.05, 0<y<0.3,and 0<z<0.1.

After the active layer for emitting light is grown according to theabove-described process steps, temperature is elevated to grow theMg-doped p-type GaN based single crystal layer 118 in H₂, N₂ and H₂+N₂gases and under NH₃ atmosphere. The p-type GaN layer 118 is grown to athickness of about 500 to 5000 Å at a growth temperature of about 900 to1020° C.

Upon the growth of the p-type GaN layer 118, the second electrodecontact layer 120 of an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super latticestructure (0<x≦0.2, and 0<y≦0.2) is grown on the p-type GaN layer 118.The In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure impartsefficient current spreading to the second electrode contact layer 120.The electrode of the second electrode contact layer can beadvantageously obtained from electrode metal the same as that of thefirst electrode contact layer 108.

According to the nitride based 3-5 group compound semiconductor lightemitting device of this embodiment, the first electrode contact layer108 is formed of an n-type electrode contact layer and the secondelectrode contact layer 120 is formed of a n-type electrode contactlayer. Since high contact resistance is originated from the low Mgdoping efficiency of a p-type GaN layer used as a second electrodecontact layer in a conventional nitride based 3-5 group compoundsemiconductor light emitting device having first and second electrodecontact layers in the form of n-type and p-type electrode contactlayers, this embodiment can overcome the high contact resistance andremove a resultant current spreading layer.

Regarding the relation with the p-type GaN layer 118, it can beexpressed that the first electrode contact layer 108, the p-type GaNlayer 118 and the second electrode contact layer 120 have an n-p-njunction.

Here, the second electrode contact layer 120 alternate with each otherat a thickness of 2 to 50 Å, and the second electrode contact layer 120has the maximum thickness under 200 Å. Also, the growing step can beperformed by feeding N₂, N₂+H₂ and NH₃ gases and TMGa and TMIn sourcesin a growth temperature range from 700 to 850° C. in order to grow ahigh brightness light emitting device having a hetero-structure which isexcellent in internal quantum efficiency and operating voltagecharacteristics.

Second Embodiment

FIG. 2 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a second embodiment ofthe present invention.

The structure of the nitride based 3-5 group compound semiconductorlight emitting device of this embodiment shown in FIG. 2 is basicallysimilar to that of the first embodiment except that anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 210 isadditionally placed underlying a first electrode contact layer 212forming a heterostructure in order to minimize crystal defectsoriginated from the mismatch of lattice constant and thermal expansioncoefficient between a substrate 202 and a Si/In-doped GaN based singlecrystal layer 212.

This structure can reduce dislocation density propagated from thesubstrate 202 and a low temperature buffer layer 204 to improve thereverse breakdown voltage Vbr of the light emitting device therebyimproving the reliability thereof.

The structure of the nitride based 3-5 group compound semiconductorlight emitting device according to the second embodiment of the presentinvention will be described in brief as follows.

The buffer layer 204 is grown on the substrate 202, and a firstelectrode contact layer 212 is made of n-type GaN (codoped with Si andIn) and a second electrode contact layer 224 is grown to have anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure. The first andsecond electrode contact layers 212 and 224 are provided with electrodes(not shown), respectively, in following process steps so that externalvoltage can be applied thereto via the electrodes.

The nitride based 3-5 group compound semiconductor light emitting deviceof the present invention also has an active layer 220 of a singlequantum well structure which is interposed between the first electrodecontact layer 212 and the second electrode contact layer 224 to form aheterostructure. The active layer 220 includes a low mole In-dopedIn_(x)Ga_(1−x)N layer 214, an In_(x)Ga_(1−y)N well layer 216 and anIn_(x)Ga_(1−x)N barrier layer 218.

In addition, the nitride based 3-5 group compound semiconductor lightemitting device also has an In-doped GaN layer 206 and an undoped GaNlayer 208 between the buffer layer 204 and the first electrode contactlayer 212. A p-type GaN layer 222 is also formed between theIn_(x)Ga_(1−x)N barrier layer 218 and the second electrode contact layer224.

A fabrication method of the nitride based 3-5 group compoundsemiconductor light emitting device having the above-described structureis similar to that of the first embodiment, and therefore will not bedescribed further.

The second embodiment of this structure can reduce dislocation densitypropagated from the substrate 202 and the buffer layer 204 to improvethe reverse breakdown voltage Vbr of the light emitting device andtherefore to improve the reliability thereof.

Third Embodiment

FIG. 3 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a third embodiment ofthe present invention.

Referring to FIG. 3, this embodiment is generally similar to the firstembodiment except that an In-doped GaN layer 318 is additionallyinterposed between a p-type GaN layer 320 and an In_(z)Ga_(1−z)N barrierlayer 314 to form a heterostructure.

The additional In-doped GaN layer 318 can restrain the in-diffusion ofMg atoms used as dopant in the p-type GaN layer 320 thereby improvingcharacteristics. The In-doped GaN layer 318 is grown to a thickness of100 Å or less.

Hereinafter a fabrication method of the semiconductor light emittingdevice of the third embodiment will be described. A buffer layer 304 isgrown on a substrate 302, a first electrode contact layer 308 is made ofan n-type GaN (codoped with Si and In), and a second electrode contactlayer 322 is formed of an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super latticestructure. Herein, the first and second electrode contact layers 308 and322 are provided with electrodes (not shown), respectively, in followingprocess steps so that external voltage can be applied thereto via theelectrodes.

The nitride based 3-5 group compound semiconductor light emitting deviceof the present invention also has an active layer 316 of a singlequantum well structure which is interposed between the first electrodecontact layer 308 and the second electrode contact layer 322 to form aheterostructure. The active layer 316 includes a low mole In-dopedIn_(x)Ga_(1−x)N layer 310, an In_(x)Ga_(1−y)N well layer 312 and anIn_(x)Ga_(1−x)N barrier layer 314.

In addition, the nitride based 3-5 group compound semiconductor lightemitting device also has an In-doped GaN layer 306 between the bufferlayer 304 and the first electrode contact layer 308, and the p-type GaNlayer 320 and the In-doped GaN layer 318 are placed between theIn_(z)Ga_(1−z)N barrier layer 314 and the second electrode contact layer322.

As described above, the additional GaN layer 318 of this embodiment canrestrain the in-diffusion of Mg atoms used as dopant in the p-type GaNlayer 320. This embodiment can improve characteristics of the lightemitting device.

Fourth Embodiment

FIG. 4 illustrates a structure of a nitride based 3-5 group compoundsemiconductor light emitting device according to a fourth embodiment ofthe present invention.

Many parts of the fourth embodiment are the same as those of the thirdembodiment except that an In-doped GaN layer 406, anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 408, anIn-doped GaN layer 412 and an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure layer 414 are additionally provided. TheIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 408, theIn-doped GaN layer 412 and the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure layer 414 function to minimize crystal defectsoriginated from the mismatch of lattice constant and thermal expansioncoefficient from a substrate 402. Further, theIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 408 canreduce dislocation density propagated from the substrate 402 and a lowtemperature buffer layer 404 to improve the reverse breakdown voltageVbr of the light emitting device.

Hereinafter a fabrication method of the semiconductor light emittingdevice of this embodiment will be described in detail with reference toFIG. 4.

The GaN-based semiconductor buffer layer 404 is grown on the sapphiresubstrate 402 at a low growth temperature. At the low growthtemperature, the buffer layer 404 of the GaN-based semiconductor can beformed of an InGaN/GaN super lattice structure and a structure ofIn_(x)Ga_(1−x)N/GaN and Al_(x)In_(y)Ga_(1−x,y)N/In_(x)Ga_(1−x)N/GaN.

The buffer layer 404 formed on the substrate 402 as above canefficiently restrict crystal defects induced from the mismatch ofthermal expansion coefficient and lattice constant between the substrate402 and a GaN based single crystal layer grown on the substrate 402,thereby producing a high quality GaN-based semiconductor.

Then, the In-doped GaN layer 406 is grown on the buffer layer 404 at ahigh growth temperature, and the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure layer 408 is additionally formed on the In-doped GaNlayer 408 in order to minimize crystal defects originated from themismatch of lattice constant and thermal expansion coefficient from thesubstrate 402.

This structure can reduce dislocation density propagated from thesubstrate 402 and the low temperature buffer layer 404 to improve thereverse breakdown voltage Vbr of the light emitting device therebyimproving the reliability thereof.

Also, the In-doped GaN layer 412 and the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)Nsuper lattice structure layer 414 are additionally formed on theIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 408 inorder to further reduce crystal defects.

Then, a Si/In-codoped GaN layer 416 is grown on theIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer 414. TheSi/In-codoped GaN layer 416 is used as a first electrode contact layer.

After that, a single quantum well layer is formed in an active layer 424for emitting a desired wavelength range of light. More particularly, alow mode In-doped In_(x)Ga_(1−x)N layer 418 (0<x≦0.2) is first grown inthe active layer 424 in order to improve the internal quantum efficiencyof the active layer 424. A quantum well structure including anIn_(y)Ga_(1−y)N well layer 420 and an In_(z)Ga_(1−z)N barrier layer 422of different In content are grown on the low mole In-dopedIn_(x)Ga_(1−x)N layer 418 to complete the active layer.

In the growing step, the active layer 424 of the single quantum wellstructure including the low mole In-doped In_(x)Ga_(1−x)N layer 418, theIn_(y)Ga_(1−y)N well layer 420 (0<y≦0.35) and the In_(z)Ga_(1−z)Nbarrier layer 422 (0<z≦0.2) are grown by feeding N₂ and H₂+N₂ gases andTMGa, TMIn and TMAl sources under NH₃ atmosphere. The low moleIn_(x)Ga_(1−x)N layer 418 has a thickness of about 10 to 500 Å, and itssurface is uniformly grown in a spiral mode.

The InGaN well layer 420 for emitting light is grown to a thickness of10 to 40 Å and the InGaN barrier layer 422 is grown to a thickness of 50to 500 Å at a growth temperature of about 700 to 800° C. In addition, inorder to realize high brightness light emitting device performance, itis necessary to maintain the uniform spiral mode from the surface of thelow mole In-doped In_(x)Ga_(1−x)N layer 418 to the In_(z)Ga_(1−z)Nbarrier layer 422. If the above growth conditions are satisfied, apractical high brightness light emitting device can be fabricatedthrough the formation of an active layer having a single quantum wellstructure as well as that having a multiple quantum well structure.

After the growth of the light-emitting active layer, the In-doped GaNlayer 426 and a Mg-doped p-type GaN GaN based single crystal layer 428are grown. The p-type GaN layer 428 is grown to a thickness of about 500to 5000 Å at a growth temperature of about 900 to 1020° C.

Then, after the p-type GaN layer 428 is grown, a second electrodecontact layer 430 of an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super latticestructure (0<y≦0.2, and 0<x≦0.2) is grown on the p-type GaN layer 428.Advantageously, the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super latticestructure can effectuate the current spreading of the second electrodecontact layer 430, The electrode of the second electrode contact layercan be advantageously obtained from electrode metal the same as that ofthe first electrode contact layer 416.

According to the nitride based 3-5 group compound semiconductor lightemitting device of this embodiment, the first electrode contact layer416 is formed of an n-type electrode contact layer and the secondelectrode contact layer 430 is formed of a n-type electrode contactlayer. Since high contact resistance is originated from the low Mgdoping efficiency of a p-type GaN layer used as a second electrodecontact layer in a conventional nitride based 3-5 group compoundsemiconductor light emitting device having first and second electrodecontact layers in the form of n-type and p-type electrode contactlayers, this embodiment can overcome the high contact resistance andremove a resultant current spreading layer.

Regarding the relation with the p-type GaN layer 428, it can beexpressed that the first electrode contact layer 416, the p-type GaNlayer 428 and the second electrode contact layer 430 have an n-p-njunction. The super lattice structure layers of the second electrodecontact layer 430 alternate with each other at a thickness of 2 to 50 Å,and the second electrode contact layer 430 has the maximum thicknessunder 200 Å. Also, the growing step can be performed by feeding N₂,N₂+H₂ and NH₃ gases and TMGa and TMIn sources in a growth temperaturerange from 700 to 850° C. in order to grow a high brightness lightemitting device having a hetero-structure excellent in internal quantumefficiency and operating voltage characteristics.

INDUSTRIAL APPLICABILITY

According to the nitride based 3-5 group compound semiconductor lightemitting device and its fabrication method of the present invention asset forth above, it is possible to effectively restrain crystal defectsoriginated from the mismatch of thermal expansion coefficient andlattice constant between a substrate of for example sapphire and a GaNGaN based single crystal layer grown thereon thereby to grow highquality GaN-based semiconductors. In particular, anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure is placedunderlying a Si/In-codoped GaN layer used as a first electrode contactlayer thereby to further restrain crystal defects.

Also, a low mole In-doped In_(x)Ga_(1−x)N is added in order to raise theinternal quantum efficiency of an active layer thereby uniformlycontrolling the growth mode of a quantum well. Since theIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure is used as asecond electrode contact layer, operating voltage can be reduced. As aconsequence, the present invention can advantageously reduce crystaldefects of a nitride based 3-5 group compound semiconductor lightemitting device as well as improve the crystallinity of a GaN GaN basedsingle crystal layer, thereby improving the performance and reliabilityof the nitride based 3-5 group compound semiconductor light emittingdevice.

1. A nitride based 3-5 group compound semiconductor light emittingdevice comprising: a substrate; a buffer layer formed above thesubstrate; a first In-doped GaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer formedabove the first In-doped GaN layer; a first electrode contact layerformed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer, the first electrode contact layer comprising a Si/In-codoped GaNlayer; an active layer formed above the first electrode contact layerand functioning to emit light; a second In-doped GaN layer; a GaN layerformed above the second In-doped GaN layer; and a second electrodecontact layer formed above the GaN layer; wherein the active layercomprises a single or multiple quantum well structure, including a lowmole In-doped In_(x)Ga_(1−x)N layer, and In_(y)Ga_(1−y)N well layer andan In_(z)Ga_(1−z)N barrier layer, and the low mole In-dopedIn_(x)Ga_(1−x)N layer has an In content smaller than that of theIn_(z)Ga_(1−z)N barrier layer.
 2. The device according to claim 1,wherein the second electrode contact layer is an n-type electrodecontact layer.
 3. The device according to claim 1, wherein the bufferlayer comprises one selected from the group consisting of an InGaN/GaNsuper lattice structure, an In_(x)Ga_(1−x)N/GaN structure and anAl_(x)In_(y)Ga_(1−x,y)N/In_(x)Ga_(1−x)N/GaN structure.
 4. The deviceaccording to claim 1, wherein the active layer comprises a single ormultiple quantum well structure.
 5. A nitride based 3-5 group compoundsemiconductor light emitting device comprising: a substrate; a bufferlayer formed above the substrate; a first In-doped GaN layer formedabove the buffer layer; an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super latticestructure layer formed above the first In-doped GaN layer; a firstelectrode contact layer formed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)Nsuper lattice structure layer; an active layer formed above the firstelectrode contact layer and functioning to emit light; a second In-dopedGaN layer; a GaN layer formed above the second In-doped GaN layer; and asecond electrode contact layer formed above the GaN layer, wherein theactive layer comprises a single or multiple quantum well structure,including a low mole In-doped In_(x)Ga_(1−x)N layer, anIn_(y)Ga_(1−y)well layer and an In_(z)Ga_(1−z)N barrier layer, and thelow mole In-doped In_(x)Ga_(1−x)N layer has an In content smaller thanthat of the In_(z)Ga_(1−z)N barrier layer.
 6. A nitride based 3-5 groupcompound semiconductor light emitting device comprising: a substrate; abuffer layer formed above the substrate; a first In-doped GaN layerformed above the buffer layer; an In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure layer formed above the first In-doped GaN layer; afirst electrode contact layer formed above theIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer; an activelayer formed above the first electrode contact layer and functioning toemit light; a second In-doped GaN layer; a GaN layer formed above thesecond In-doped GaN layer; and a second electrode contact layer formedabove the GaN layer, wherein the active layer comprises a single ormultiple quantum well structure, including a low mole In-dopedIn_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)N well layer and anIn_(z)Ga_(1−z)N barrier layer, and the low mole In-doped In_(x)Ga_(1−x)Nlayer, the In_(y)Ga_(1−y)N well layer and the In_(z)Ga_(1−z)N barrierlayer have an In content expressed as 0<x<0.05, 0<y<0.3 and 0<z<0.1,respectively.
 7. The device according to claim 1, wherein the low moleIn-doped In_(x)Ga_(1−x)N layer has a spiral surface configuration. 8.The device according to claim 1, wherein the low mole In-dopedIn_(x)Ga_(1−x)N layer has a spiral surface configuration, and whereinthe spiral surface configuration is extended to the surface of theIn_(z)Ga_(1−z)N barrier layer.
 9. The device according to claim 1,wherein the second electrode contact layer comprises anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure.
 10. A nitridebased 3-5 group compound semiconductor light emitting device comprising:a substrate; a buffer layer formed above the substrate; a first In-dopedGaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer formedabove the first In-doped GaN layer; a first electrode contact layerformed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer; an active layer formed above the first electrode contact layerand functioning to emit light; a second In-doped GaN layer; a GaN layerformed above the second In-doped GaN layer; and a second electrodecontact layer formed above the GaN layer, wherein the first In-doped GaNlayer and the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer formed thereon are repeatedly layered in plurality.
 11. A nitridebased 3-5 group compound semiconductor light emitting device comprising:a substrate; a buffer layer formed above the substrate; a first In-dopedGaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer formedabove the first In-doped GaN layer; a first electrode contact layerformed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer, the first electrode contact layer comprising a Si/In-codoped GaNlayer; an active layer formed above the first electrode contact layerand functioning to emit light; a GaN layer formed above the activelayer; and a second electrode contact layer formed above the GaN layer.12. The device according to claim 11, wherein the second electrodecontact layer is an n-type electrode contact layer.
 13. The deviceaccording to claim 11, further comprising a second In-doped GaN layerformed between the active layer and the GaN layer, and the GaN layer isp-type.
 14. A nitride based 3-5 group compound semiconductor lightemitting device comprising: a substrate; a buffer layer formed above thesubstrate; a first In-doped GaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure layer formedabove the first In-doped GaN layer; a first electrode contact layerformed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structurelayer; an active layer formed above the first electrode contact layerand functioning to emit light; a GaN layer formed above the activelayer; and a second electrode contact layer formed above the GaN layer.15. A nitride based 3-5 group compound semiconductor light emittingdevice comprising: a substrate; a buffer layer formed above thesubstrate; a first In-doped GaN layer formed above the buffer layer; anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure and an undopedGaN layer formed above the first In-doped GaN layer; a first electrodecontact layer formed above the In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N superlattice structure and an undoped GaN layer; an active layer formed abovethe first electrode contact layer and functioning to emit light; a GaNlayer formed above the active layer; and a second electrode contactlayer formed above the GaN layer.
 16. The device according to claim 11,wherein the buffer layer comprises one selected from the groupconsisting of an InGaN/GaN super lattice structure, anIn_(x)Ga_(1−x)N/GaN structure and anAl_(x)In_(y)Ga_(1−x,y)N/In_(x)Ga_(1−x)N/GaN structure.
 17. The deviceaccording to claim 11, wherein the active layer comprises a single ormultiple quantum well structure.
 18. The device according to claim 11,wherein the active layer comprises a single or multiple quantum wellstructure, including a low mole In-doped In_(x)Ga_(1−x)N layer, anIn_(y)Ga_(1−y)N well layer and an In_(z)Ga_(1−z)N barrier layer.
 19. Anitride based 3-5 group compound semiconductor light emitting devicecomprising: a substrate; a buffer layer formed above the substrate; afirst In-doped GaN layer formed above the buffer layer; a firstelectrode contact layer formed above the first In-doped GaN layer; anactive layer formed above the first electrode contact layer andfunctioning to emit light; a GaN layer formed above the active layer;and a second electrode contact layer formed above the GaN layer, whereinthe active layer comprises a single or multiple quantum well structure,including a low mole In-doped In_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)Nwell layer and an In_(z)Ga_(1−z)N barrier layer, and the low moleIn-doped In_(x)Ga_(1−x)N layer has an In content smaller than that ofthe In_(z)Ga_(1−z)N barrier layer.
 20. A nitride based 3-5 groupcompound semiconductor light emitting device comprising: a substrate; abuffer layer formed above the substrate; a first In-doped GaN layerformed above the buffer layer; a first electrode contact layer formedabove the first In-doped GaN layer; an active layer formed above thefirst electrode contact layer and functioning to emit light; a GaN layerformed above the active layer; and a second electrode contact layerformed above the GaN layer, wherein the active layer comprises a singleor multiple quantum well structure, including a low mole In-dopedIn_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)N well layer and anIn_(z)Ga_(1−z)N barrier layer, and the low mole In-doped In_(x)Ga_(1−x)Nlayer, the In_(y)Ga_(1−y)N well layer and the In_(z)Ga_(1−z)N barrierlayer have an In content expressed as 0<x<0.05, 0<y<0.3 and 0<z<0.1,respectively.
 21. The device according to claim 20, wherein the low moleIn-doped In_(x)Ga_(1−x)N layer has a spiral surface configuration. 22.The device according to claim 20, wherein the low mole In-dopedIn_(x)Ga_(1−x)N layer has a spiral surface configuration, and whereinthe spiral surface configuration is extended to the surface of theIn_(z)Ga_(1−z)N barrier layer.
 23. The device according to claim 20,wherein the second electrode contact layer comprises anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N super lattice structure.
 24. A nitridebased 3-5 group compound semiconductor light emitting device comprising:a substrate; a buffer layer formed above the substrate; a firstelectrode contact layer formed above the buffer layer; an active layerformed above the first electrode contact layer, and including a low moleIn-doped In_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)N well layer and anIn_(z)Ga_(1−z)N barrier layer; a GaN layer formed above the activelayer; and a second electrode contact layer formed above the GaN layer,wherein the low mole In-doped In_(x)Ga_(1−x)N layer has an In contentsmaller than that of the In_(z)Ga_(1−z)N barrier layer.
 25. A nitridebased 3-5 group compound semiconductor light emitting device comprising:a substrate; a buffer layer formed above the substrate; a firstelectrode contact layer formed above the buffer layer; an active layerformed above the first electrode contact layer, and including a low moleIn-doped In_(x)Ga_(1−x)N layer, an In_(y)Ga_(1−y)N well layer and anIn_(z)Ga_(1−z)N barrier layer; a GaN layer formed above the activelayer; and a second electrode contact layer formed above the GaN layer,wherein the low mole In-doped In_(x)Ga_(1−x)N layer, the In_(y)Ga_(1−y)Nwell layer and the In_(z)Ga_(1−z)N barrier layer have an In contentexpressed as 0<x<0.05, 0<y<0.3 and 0<z<0.1, respectively.
 26. The deviceaccording to claim 25, wherein the low mole In-doped In_(x)Ga_(1−x)Nlayer has a spiral surface configuration.
 27. The device according toclaim 25, wherein the low mole In-doped In_(x)Ga_(1−x)N layer has aspiral surface configuration, wherein the spiral surface configurationis extended to the surface of the In_(z)Ga_(1−z)N barrier layer.